In modern society, electronic devices represented by a computer, a smart phone and the like spread, the Internet is connected all over the world, and much information is exchanged. Up to now, such information has been mainly information created by human work in many cases. However, for more comfortable life, activities in which every data in real society is captured by sensors and utilized are carried out. In the near future, it is said that times of what is called “a trillion sensors” come, and it is desired that various data of environment, traffic, a condition of health, an appearance of exchange, and the like are collected to be utilized. For this purpose, a large number of various sensors become necessary, so that development of new sensors is actively progressing.
As one of the above sensors, there is a gas sensor. The gas sensor is desired not only to serve as environmental monitoring by detecting one such as, for example, a nitrogen oxide but also to enable utilization for monitoring the condition of health by detecting components of an expired gas, a skin gas, and the like produced from a human body.
[Patent Document 1] Japanese Patent No. 3555739
[Non-Patent Document 1] J. Cai et al., Nature 466 (2010) 470.
As gases necessary to be detected for health care, there are various ones such as, for example, ammonia, nonanal, methane, and acetone. In order to sense such various gases, there is a need to prepare a plurality of highly-sensitive gas sensors whose sensitivities are different for the respective gases. Under the present situation, a gas sensor utilizing an oxide semiconductor such as SnO2 is used for sensing the ammonia and the like. However, the sensitivity of the above gas sensor is about dozens ppm, which is far less than the sensitivity necessary for sensing an organism gas (about ppb), and in addition, gas selectivity is also insufficient.